The Hair Bulb
The hair bulb is a compact, elongate structure, located in the dermis, composed of three main cellular groups:
(i) a compact group of fibroblasts including a capillary system known as the dermal papilla;
(ii) surrounding epithelial tissue, a component of which proliferates and differentiates to give rise to the mature hair shaft, and
(iii) a group of fibroblasts present around the outside of the bulb in the connective tissue sheath.
It is well recognised that the dermal papilla is essential for hair growth [Oliver R F (1970) J Embryol Exp Morphol 23, 219-236] and that, consequently, it is also essential for the proliferation of the adjacent epithelial cells which give rise to hair.